Wave-induced water particle motion measurements

Abstract

Simultaneous measurements of wave height and two orthogonal water particle velocities were made at six elevations in nineteen meters of water using a penetrating wave staff and an electromagnetic flowmeter. Moderate swell and low wind conditions prevailed during the experiment. The mea­sured wave-induced velocities were two to four percent greater than those predicted using linear wave theory. Coherence of the wave height and wave-induced velocities in the significant energy-density range was computed to be over 0.85, indicating that the motion was almost totally wave induced. At higher frequencies it was apparent that the motion was primarily turbulence. Phase spectra computed for the measured wave heights and orbital velocities compared very well with linear theory. Measured frequency distributions were compared to both Gaussian and Gram-Charlier distributions using the chi-squared goodness-of-fit test. Qualitatively, the Gram-Charlier distribution gave the better fit to the data.